Q. Hu et al., INHIBITION OF TOOSENDANIN ON THE DELAYED RECTIFIER POTASSIUM CURRENT IN NEUROBLASTOMA X GLIOMA NG108-15 CELLS, Brain research, 751(1), 1997, pp. 47-53
The effect of Toosendanin (TSN), a presynaptic transmission blocker, o
n the outward delayed rectifier potassium current (I-KD) of NG108-15 c
ells was studied by using the whole-cell voltage-clamp technique. It w
as observed that externally applying TSN not only reduced I-KD amplitu
de in a dose-dependent and partial reversible manner but also accelera
ted its inactivation. The effect of internally applying TSN was also e
xamined by including TSN in the electrode, and it was the same as that
of externally applying TSN. Further, comparison observations with TEA
, 4-AP, verapamil, nifedipine, and(+/-)-Bay K 8644 were also made, and
the results were as follows. The time courses of TSN's inhibition eff
ect as well as its recovery after washing were much slower than those
of TEA and 4-AP. Externally applying TEA or 4-AP reduced I-KD amplitud
e but did not accelerate its inactivation. Externally applying verapam
il, nifedipine, or (+/-)-Bay K 8644, however, similarly to the effect
of TSN, not only reduced I, amplitude but also accelerated its inactiv
ation. Thus, from the obtained results it is suggested that TSN might
diffuse into the cell interior and act intracellularly, and the underl
ying mechanism might be different from that of TEA and 4-AP but simila
r to that of verapamil, nifedipine, and (+/-)-Bay K 8644 to some exten
t. (C) 1997 Elsevier Science B.V.